Because two-way video communications can give individuals the ability to communicate graphical information and to see facial expressions and gestures that cannot be conveyed by audio alone, much emphasis has been placed on commercial development of such systems. Indeed, video telephones that work with analog telephone lines have been demonstrated. However, due to the limited bandwidth of conventional telephone lines, and the consequent limitation on the amount of information that can be carried therethrough, commercial development has been limited to less-than-full-motion video presented on a small display.
In order to overcome the bandwidth limitation associated with video telephony transmitted over the analog telephone lines, video telephones more recently have been designed to work with digital telephone access lines, such as ISDN. However, at the present time, digital access facilities to consumer homes are not readily available.
Other systems use optical fiber directly linked to subscriber homes in order to obtain the high bandwidth needed for full motion video. However, these facilities are expensive, and thus are not accessible to the ordinary household. Besides, it will be decades before most homes are provided with fiber access.
The above-outlined problems are substantially ameliorated by the arrangement disclosed in the co-pending, commonly assigned United States patent application of C. D. Yu entitled "Bidirectional Video Telephony Using Shared Channels on Coaxial Cable Networks," Ser. No. 787,436, filed Nov. 4, 1991. In a disclosed embodiment of the Yu arrangement, the terminal equipment comprises a standard television set, serving as the audio/video display, and a consumer-type camera or camcorder, serving as the audio/video source. A coaxial cable network, which is preferably a part of an existing cable television system, provides a local access link for the transmission of the video telephone signals between each originating and destination cable subscriber location and a respective "head end" located on the cable company premises. A network interface unit, or NIU, at each location provides a control interface between the terminal equipment and the cable television distribution network to deal with such "housekeeping" chores as allocation of upstream and downstream video telephone channels between the subscriber location and the head end, receiving of "dialing" information from the subscriber, etc. Each of the head ends is connected to a "point of presence" of a telephone common carrier-illustratively an interexchange carrier such as AT&T-so that a connection between pairs of head ends, and thus between a pair of video telephone locations, can be made via a switched network maintained by the carrier.